I'm no Plumber but it's my understanding that the differences are many.
One is: You DON'T use DWV pipe for fresh water lines. DWV is EXCLUSIVELY for Drain Waste.
PVC simply stands for PolyVinyl Chloride. This is the material that the pipe is made of. DWV (Drain, Waste, and Vent) piping vs. PVC for, say, water delivery differ in that DWV is NOT for use under pressure and the other is. Even the 'glues' are different when connecting the pipe. The thickness is different too (since DWV pipe is not used under pressure.) For future reference, just make sure that you're told that the pipe you want is the pipe for the job.
RE: Correcting the landscape at the foundation - You are correct in that you shouldn't set any dirt to within 6" of the TOP of the foundation. Violating this would 'encourage' termites and other bugs to enter the house. When it comes to plants and such being at the foundation, my recommended rule of thumb is that nothing should be 'growing' within 2' of the foundation. This 'breathing room' allows air to flow unobstructed all around the house (to dry the ground), and this area allows the sun to get there (if possible to assist in drying the ground), and also for maintenance of not only the plants but of the house too. What most homeowners do is plant a plant near the foundation W/O realizing that when when it's 'full grown', it's TOO close to the house. So, in short, for example, if you want a bush to stay 2' from the foundation, and at its FULLEST (3 years from planting) it's 2' in diameter, then plant it 3' from the foundation. The math for planting is: 1/2 the diameter of the FULLEST size of the plant, divided by 2, plus 2'. THAT'S where the plant should be planted. Of course, in this example, for the 1st 2-3 years of growth, the bush is going to look a little 'out of place' because it's so far from the house. BUT, when it gets to FULL GROWTH (or to that point where you start pruning it), it will be 2' from the foundation! See how that works? Oh, if you keep to the 6" rule and the plant rule, you'll be OK to keep mulch down. The ground UNDER the mulch will be kept damp as long as you keep the mulch about 3"+ in depth. This means you may need to add more mulch in mid-Summer. (I have a flower bed out front of the house and laid down 4" of shredded bark in April. By June, it was 'compressed' to about 2" and I had to add 3" more. That was just fine for the entire summer.)
RE: The Mold on the basement wall - Yes, be sure your gutter, downspout, and landscaping sloping 'issues' are OK. (Do that 'don the raincoat thing to check it all.) Once you've made your fixes and re-doned another rainstorm, go ahead and clean the wall. 90% of all basement water issues are solved with gutter, downspout, and landscaping 'fixes'. From the sounds of it 'over here', your troubles should go away once you fix any/all of the aforementioned.
For now, my best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!